moving UDP payload size to config option, improve throughput performance

moving UDP payload size to optional config choice to imporove throughput performance

etc/config.sample.toml

@@ -330,6 +330,7 @@ reporting-disabled = false
   # batch-pending = 5 # number of batches that may be pending in memory
   # batch-timeout = "1s" # will flush at least this often even if we haven't hit buffer limit
   # read-buffer = 0 # UDP Read buffer size, 0 means OS default. UDP listener will fail if set above OS max.
+  # udp-payload-size = 1500 # set the expected UDP payload size, default: 65536
 
 ###
 ### [continuous_queries]

services/udp/config.go

@@ -31,6 +31,24 @@ const (
 	//     Linux:      sudo sysctl -w net.core.rmem_max=<read-buffer>
 	//     BSD/Darwin: sudo sysctl -w kern.ipc.maxsockbuf=<read-buffer>
 	DefaultReadBuffer = 0
+
+	// DefaultUDPPayloadSize sets the default value of the incoming UDP packet
+	// to the spec max, i.e. 65536. That being said, this value should likely
+	// be tuned lower to match your udp_payload size if using tools like
+	// telegraf.
+	//
+	// https://en.wikipedia.org/wiki/User_Datagram_Protocol#Packet_structure
+	//
+	// Reading packets from a UDP socket in golang actually only pulls
+	// one packet at a time, requiring a very fast reader to keep up with
+	// incoming data at scale. Reducing the overhead of the expected packet
+	// helps allocate memory faster (~10-25µs --> ~150ns with go1.5.2), thereby
+	// speeding up the processing of data coming in.
+	//
+	// NOTE: if you send a payload greater than the UDPPayloadSize, you will
+	// cause a buffer overflow...tune your application very carefully to match
+	// udp_payload for your metrics source
+	DefaultUDPPayloadSize = 65536
 )
 
 // Config holds various configuration settings for the UDP listener.
@@ -44,6 +62,7 @@ type Config struct {
 	BatchPending    int           `toml:"batch-pending"`
 	ReadBuffer      int           `toml:"read-buffer"`
 	BatchTimeout    toml.Duration `toml:"batch-timeout"`
+	UDPPayloadSize  int           `toml:"udp-payload-size"`
 }
 
 // WithDefaults takes the given config and returns a new config with any required
@@ -65,5 +84,8 @@ func (c *Config) WithDefaults() *Config {
 	if d.ReadBuffer == 0 {
 		d.ReadBuffer = DefaultReadBuffer
 	}
+	if d.UDPPayloadSize == 0 {
+		d.UDPPayloadSize = DefaultUDPPayloadSize
+	}
 	return &d
 }

services/udp/config_test.go

@@ -19,6 +19,7 @@ retention-policy = "awesomerp"
 batch-size = 100
 batch-pending = 9
 batch-timeout = "10ms"
+udp-payload-size = 1500
 `, &c); err != nil {
 		t.Fatal(err)
 	}
@@ -38,5 +39,7 @@ batch-timeout = "10ms"
 		t.Fatalf("unexpected batch pending: %d", c.BatchPending)
 	} else if time.Duration(c.BatchTimeout) != (10 * time.Millisecond) {
 		t.Fatalf("unexpected batch timeout: %v", c.BatchTimeout)
+	} else if c.UDPPayloadSize != 1500 {
+		t.Fatalf("unexpected udp-payload-size: %d", c.UDPPayloadSize)
 	}
 }

services/udp/service.go

@@ -18,10 +18,6 @@ import (
 )
 
 const (
-	// UDPBufferSize is the maximum UDP packet size
-	// see https://en.wikipedia.org/wiki/User_Datagram_Protocol#Packet_structure
-	UDPBufferSize = 65536
-
 	// Arbitrary, testing indicated that this doesn't typically get over 10
 	parserChanLen = 1000
 )
@@ -163,7 +159,7 @@ func (s *Service) serve() {
 			return
 		default:
 			// Keep processing.
-			buf := make([]byte, UDPBufferSize)
+			buf := make([]byte, s.config.UDPPayloadSize)
 			n, _, err := s.conn.ReadFromUDP(buf)
 			if err != nil {
 				s.statMap.Add(statReadFail, 1)